1. Field of the Invention
This invention is generally related to monitoring insulation of an electrically insulated DC network.
2. Description of the Related Art
DE 43 39 946 A1 is directed to a method and apparatus for insulation monitoring of an electrically insulated DC network that supplies DC loads and/or AC loads via an inverter, and which possesses an unavoidable ohmic and capacitive insulation resistance with respect to earth or ground. A series connection of one AC pulse voltage source and one measuring resistor is coupled to the DC network and to earth or ground. The AC pulse voltage source applies an AC pulse voltage with alternating positive and negative polarity to the measuring resistor. The measuring process is only enabled after a certain time delay following the application of the AC pulse voltage to the measuring resistor. Measurement values of voltage drops at the measuring resistor obtained in successive time intervals are, after subtraction from each other, further processed to determine the insulation resistance.
DE 20 51 836 C2 is generally directed to a device for insulation monitoring of ungrounded DC networks. The device has a primary winding that can be alternatingly connected between two network terminals and ground or earth, a secondary winding that is electrically isolated from the primary winding and which is connected to an evaluation circuit, and a compensating winding used to compensate for network voltage fluctuations.
DE 195 03 749 C1 is directed to a vehicle with a power supply network that is fed by a fuel cell or battery and is executed as an IT network. The loads that are connected to the load circuit also have a low-resistance electrical connection to the vehicle chassis. Looped in between the load circuit and the vehicle chassis is an insulation monitoring device that includes a balancing stage for a measuring bridge and a buffer amplifier stage that processes the measurement signals. A power supply network of this type is preferably arranged in an electrical vehicle. The term IT network in this context means that all components consuming electrical current are supplied by the two lines of the load circuit, which have a high-resistance connection to the vehicle chassis, and that—as a protective measure against too high a touch potential—connects all system components to be protected to each other and to the vehicle chassis with a low resistance, for example having a saturation resistance of <1 Ω.
Many DC networks can be treated as having two or more portions. It would be advantageous to be able to monitor the insulation resistance with respect to a ground potential in each portion of a network. In particular, it would be advantageous to perform insulation monitoring independently of whether one or both network portions are connected or isolated with respect to one another, for example, by a switch.